1. Field of the Invention
This invention relates to a backlight of a display device, and more particularly to a driving apparatus of a backlight and a method of driving a backlight using the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for generating a burst dimming signal having a consistent On/Off duty cycle.
2. Description of the Related Art
In general, a liquid crystal display (LCD) device displays images by controlling optical transmittance of liquid crystal cells. An active matrix type of liquid crystal display device having a switching device provided for each liquid crystal cell is advantageous in the implementation of moving pictures because of the speed at which the switching devices can be switched. The switching devices used for the active matrix liquid crystal display devices are typically thin film transistors (TFT).
FIG. 1 is an equivalent circuit diagram of a pixel provided in the related art liquid crystal display device. The active matrix type liquid crystal display device converts a digital input data into an analog data voltage on the basis of a gamma reference voltage and then supplies the analog data voltage to a data line DL while also supplying a scanning pulse to a gate line GL to charge a liquid crystal cell Clc with the analog data voltage from the data line DL. A gate electrode of the TFT is connected to the gate line GL while a source electrode is connected to the data line DL. Further, a drain electrode of the TFT is connected to a pixel electrode of the liquid crystal cell Clc and to one electrode of a storage capacitor Cst. A common electrode of the liquid crystal cell Clc is supplied with a common voltage Vcom.
When the scanning pulse is applied to the gate line GL, then the TFT is turned on to provide a channel between the source electrode and the drain electrode, so that a voltage on the data line DL is supplied to the pixel electrode of the liquid crystal cell Clc. The storage capacitor Cst receives the analog data voltage from the data line DL when the TFT is turned on and maintains the charged analog data voltage in the liquid crystal cell Clc. The alignment state of the liquid crystal molecules is changed by an electric field between the pixel electrode and the common electrode. As a result, the optical transmittance of the liquid crystal is changed according to the changed alignment of the liquid crystal.
FIG. 2 is a block diagram showing a typical configuration of the related art liquid crystal display device. Referring to FIG. 2, the related art liquid crystal display device 100 includes a liquid crystal display panel 110 provided with a thin film transistor (TFT) for driving the liquid crystal cells Clc at each crossing of the data lines DL1 to DLm and the gate lines GL1 to GLn, a data driver 120 for supplying data to the data lines DL1 to DLm of the liquid crystal display panel 110, a gate driver 130 for supplying a scanning pulse to the gate lines GL1 to GLn of the liquid crystal display panel 110, an external power source 140 connected to the data driver 120, a timing controller 150 for controlling the data driver 120 and the gate driver 130, a backlight assembly 160 for irradiating a light to the liquid crystal display panel 110 and an inverter 170 for applying an alternating current voltage to the backlight assembly 160.
The liquid crystal display panel 110 has a liquid crystal injected between upper and lower glass substrates (not shown). On the lower glass substrate of the liquid crystal display panel 110, the data lines DL1 to DLm and the gate lines GL1 to GLn perpendicularly cross each other. At each crossing of the data lines DL1 to DLm and the gate lines GL1 to GLn, TFTs are provided. The TFTs switch data from the data lines DL1 to DLm to the liquid crystal cells Clc in response to scanning pulses. The gate electrodes of the TFTs are connected to the gate lines GL1 to GLn while the source electrodes thereof are connected to the data lines DL1 to DLm. Further, the drain electrodes of the TFTs are connected to the pixel electrodes of the liquid crystal cells Clc and to the storage capacitors Cst.
The TFT is turned on in response to the scanning pulse applied, via the gate lines GL1 to GLn, to the gate terminal thereof. Upon turning-on of the TFT, a video data on the data lines DL1 to DLm is supplied to the pixel electrode of the liquid crystal cell Clc. The timing controller 150 supplies a digital video data RGB to the data driver 120. Also, the timing controller 150 generates a data driving control signal DDC and a gate driving control signal GDC using a horizontal/vertical synchronizing signal H and V, and a clock signal CLK. The data driving control signal DDC includes a source shift clock SSC, a source start pulse SSP, a polar control signal POL and a source output enable signal SOE. The data driving control signal DDC is supplied to the data driver 120. The gate driving control signal GDC includes a gate start pulse GSP, a gate shirt clock GSC and a gate output enable GOE. The gate driving control signal GDC is supplied to the gate driver 130.
The gate driver 130 sequentially generates a scanning pulse, such as a gate high pulse, in response to the gate driving control signal GDC supplied from the timing controller 150. The gate driver 130 includes a shift register (not shown) for sequentially generating the scanning pulse and a level shifter (not shown) for shifting the swing width of the scanning pulse voltage to voltages higher than the threshold voltage of the TFTs.
The data driver 120 supplies a data to the data lines DL1 to DLm in response to the data driving control signal DDC from the timing controller 150. Further, the data driver 120 samples and latches digital video data RGB fed from the timing controller 150. Then, the data driver converts the latched digital video data RGB into an analog voltage capable of expressing a gray scale level in the liquid crystal cell Clc.
The backlight assembly 160 provided at the rear side of the liquid crystal display panel 110 radiates light to each pixel of the liquid crystal display panel 110 in response to an alternating current (AC) voltage supplied from the inverter 170. The inverter 170 converts a square wave signal generated within the inverter into a triangular wave signal and then compares the triangular wave signal with a direct current (DC) voltage supplied from an exterior electronic device, such as a controller of the image display apparatus, thereby generating a burst dimming signal proportional to a result of the comparison. Herein, if the exterior electronic device is a controller for controlling a function of the image display apparatus, then the exterior electronic device supplies the DC voltage having a value approximately 0V to 3.3V to the inverter 170. If the burst dimming signal determined in accordance with the rectangular wave signal at the interior of the inverter 170, then a driving integrated circuit IC (not shown) for controlling a generation of the AC voltage within the inverter 160 controls a generation of the AC voltage supplied to the backlight assembly 160 in response to the burst dimming signal.
When the resistance of an interior resistance element changes due to an increase in temperature within the inverter 170 of the related art driving apparatus, then the On/Off duty cycle of the square signal oscillated within the interior of the inverter 170 is also changed. Accordingly, the On/Off duty cycle of a burst dimming signal used for controlling a magnitude of the AC voltage supplied to the backlight assembly 160 is also changed. The burst dimming signal is affected by the square signal being changed by an increase in temperature within the inverter. Such changes in the burst dimming signal can cause the problem of wavy noise to be generated on the liquid crystal display panel. Also, the inverter 170 having the related art driving apparatus is not controlled by the image display apparatus. Accordingly, if an irradiating system of the image display apparatus, for example, a PAL system or an NTSC system, is changed, the inverter 170 may not oscillate the correct square wave signal for the irradiating system.